The present invention relates to a method and apparatus for compensating in temperature or heating to required temperatures the steel products such as sheets, pipes, bars, shapes and so on when they are subjected various heat-treatments such as hardening, tempering and normalizing.
In the case of heat-treatments such as hardening, tempering and normalizing the steel products, it has been a general practice to cool the rolled steel products to room temperature and then to heat them to the required temperatures of heat-treatments.
More specifically, in the case of hardening, the steel products are once cooled and then re-heated to the hardening temperatures in a heating furnace which is exterior or outside the rolling line. That is, the heating furnace must be provided and a large amount of thermal energy is needed for reheating the steel products to be hardened. In addition, since the steel products must pass through the reheating furnace, the hardening step cannot be incorporated into the rolling line.
In the case of tempering, the steel products are once cooled to room temperature and then re-heated to the required tempering temperatures. Therefore there must be installed a reheating furnace which extends over a considerably long distance. In addition, in order to heat the steel products to be tempered from room temperature to the required tempering temperatures, a large amount of thermal energy is needed. Furthermore because of the difficulty of maintaining the hardened steel products at desired temperatures levels, they are subjected to undercooling to the temperatures below the level required for martensite transformation.
In the case of normalizing, the steel products, which have been cooled, are reheated to the normalizing temperatures. Therefore as in the case of tempering, there must be installed a reheating furnace which extends over a considerably long distance, and a large amount of thermal energy is required to heat the steel products from room temperature to the normalizing temperatures.
In view of the above, the primary object of the present invention is to provide a method and apparatus for heat-treating the steel products which may reduce the thermal energy consumption to a considerably low level hitherto never attainable by any prior art methods and apparatus.
Another object of the present invention is to provide a method and apparatus for uniformly heating to the desired temperature levels for heat-treatments the steel products even when their temperature distributions are not uniform before they are charged into the heat-treatment apparatus or installation, whereby the qualities of the steel products may be improved and the saving in labor may be attained.
The above and other objects, features and advantages of the present invention will become more apparent from the following description of a preferred embodiment thereof taken in conjunction with the accompanying drawings.